ComputerNetworksAndSecurity/Codes/Code-A4.cpp

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C++
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#include <iostream>
#include <cstring>
using namespace std;
string XOR(string data, string key) {
// Dividend is data
// Divisor is the primary key, i.e. the key
string result = "";
int dataLen = data.length();
int keyLen = key.length();
// Perform XOR operation
for (int i=0; i<keyLen; i++) {
if (i < dataLen) {
// Only perform XOR if within the length of data
if (data[i] == key[i]) {
result += '0';
}
else {
result += '1';
}
} else {
// If data length exceeded, append the key
result += key[i];
}
}
return result;
}
string encoder(string data, string key) {
int keyLen = key.length();
// Append n-1 zeroes to the data
string dataWithZeroes = data + string(keyLen-1, '0');
// Perform XOR operation with the key
string remainder = XOR(dataWithZeroes, key);
// Get the remainder (last n-1 bits)
string crc = remainder.substr(remainder.length() - (keyLen-1));
// Append the CRC to the original data
return data + crc;
}
string performDivision(string data, string key) {
int keyLen = key.length();
// Initialize with the data to be divided
string temp = data.substr(0, keyLen);
// Perform XOR operations on each segment
for (int i = keyLen; i < data.length(); i++) {
if (temp[0] == '1') { // Only perform XOR if the leading bit is 1
temp = XOR(temp, key);
}
temp = temp.substr(1) + data[i]; // Shift left and add the next bit
}
// Perform the final XOR operation
if (temp[0] == '1') {
temp = XOR(temp, key);
}
// Extract the remainder (last keyLen-1 bits)
return temp.substr(temp.length() - (keyLen - 1));
}
// Function to check the correctness of received data
bool checkData(string data, string key) {
string remainder = performDivision(data, key);
return (remainder.find('1') == string::npos); // No '1' means remainder is all zeros
}
int main() {
string data, key;
cout << endl << "Enter data:\t";
getline(cin, data);
cout << "Enter primary key:\t";
getline(cin, key);
cout<<endl<<"Original data:\t"<<data;
cout<<endl<<"Key:\t"<<key;
string messageToSend = encoder(data, key);
cout<<endl<<"----------------------------------------"<<endl;
cout<<"Message to be sent:\t"<<messageToSend;
cout<<endl<<"----------------------------------------"<<endl;
string receivedData;
cout<<endl<<"HINT: Received data should be the same as message to be sent.";
cout<<endl<<"Enter received data:\t";
getline(cin, receivedData);
if (receivedData == messageToSend) {
cout<<"The received data is correct."<<endl;
} else {
cout<<"The received data appears to be tampered."<<endl;
}
return 0;
}